Selective hydrodesulfurization catalyst

ABSTRACT

This invention relates to a catalyst and process for selectively hydrodesulfurizing naphtha feedstreams using a catalyst comprising at least one hydrodesulfurizing metal supported on a low acidity, ordered mesoporous support material.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims benefit of U.S. Provisional Patent ApplicationSer. No. 60/606,005 filed Aug. 31, 2004.

FIELD OF THE INVENTION

The present invention relates to a catalyst and process for selectivelyhydrodesulfurizing naphtha feedstreams using a catalyst comprising atleast one hydrodesulfurizing metal supported on a low acidity, orderedmesoporous support material.

BACKGROUND OF THE INVENTION

Gasoline comprises naphtha boiling-range hydrocarbons (“naphtha”)obtained from natural and/or synthetic sources. Naphtha, especiallynaphtha obtained from a cracking process, such as fluidized catalyticcracking and coking, typically contains undesirable sulfur species.However, naphtha also can contain valuable olefins which contribute tothe octane number of the resulting gasoline, and it is, consequently,highly desirable not to saturate them to lower octane paraffins duringprocessing. Continuing regulatory pressure to lower the amount of sulfurpresent in naphtha has resulted in a continuing need for catalystshaving ever-improved desulfurization properties. While conventional(i.e., known to those skilled in the art of naphtha desulfurization)hydrodesulfurization catalysts are available, there is a continuing needfor improved catalysts that are capable of combininghydrodesulfurization without undue olefin saturation.

SUMMARY OF THE INVENTION

In an embodiment, the invention relates to a selectivehydrodesulfurization catalyst comprising at least one hydrodesulfurizingmetal supported on a low acidity, ordered mesoporous support materialand bound with a silica binder derived from silicone resin.

In another embodiment, the invention relates to a selectivehydrodesulfurization process, comprising:

-   -   contacting a naphtha feedstream containing sulfur and olefin        with a catalytically effective amount of a catalyst comprising        at least one hydrodesulfurizing metal supported on a low        acidity, ordered mesoporous support material under selective        catalytic hydrodesulfurization conditions.

Yet another embodiment of the invention relates to a selectivehydrodesulfurization process, comprising:

-   -   contacting a naphtha feedstream containing sulfur and olefin        with a catalytically effective amount of a catalyst comprising        at least one hydrodesulfurizing metal supported on a low        acidity, ordered mesoporous support material and silica binder        derived from silicone resin under selective catalytic        hydrodesulfurizing conditions.

In yet another embodiment, the invention relates to a selectivehydrodesulfurization catalyst comprising at least one hydrodesulfurizingmetal supported on a low acidity, ordered mesoporous support material,the selective hydrodesulfurization catalyst being made by a processcomprising:

-   -   (a) combining the low acidity, ordered mesoporous support        material with silicone resin to form a mixture of mesoporous        support material and silicone resin,    -   (b) calcining the mixture from step (a) to convert silicone        resin to silica binder,    -   (c) impregnating the calcined low acidity, ordered mesoporous        support material from step (b) with an aqueous precursor        containing at least one metal to form a metal-impregnated, low        acidity, ordered mesoporous support material; and    -   (d) heating the calcined metal-impregnated, low acidity,        ordered, mesoporous support material from step (c) at a drying        temperature and drying pressure and for a drying time to remove        water and form a dried, metal-impregnated, low acidity, ordered        mesoporous support material. In a preferred embodiment, the        combining of ordered mesoporous support material with silicone        resin is free of added organic solvent.

In an embodiment, the process further comprises sulfiding themetal-impregnated low acidity, ordered mesoporous support undersulfiding conditions for a sulfiding time to form the selectivehydrodesulfurization catalyst.

BRIEF DESCRIPTION OF THE DRAWING

The FIGURE is a graph showing the rate ratio ofhydrodesulfurization/olefin saturation vs. amount ofhydrodesulfurization for two catalysts having different supportacidities.

DETAILED DESCRIPTION OF THE INVENTION

The invention relates to (I) a selective hydrodesulfurization catalyst,(II) a selective hydrodesulfurization process, and (III) method formaking a selective hydrodesulfurization catalyst.

(I) Selective Hydrodesulfurization Catalysts

In one embodiment, the invention relates to a selectivehydrodesulfurization catalyst comprising at least one catalytic metalsupported on a low acidity, ordered mesoporous support material andbound with a silica binder. As used herein, the terms “macropores” and“mesopores” are as defined in Pure Appl. Chem., 45 (1976), 79, namely aspores whose diameter is above 50 nm (macropores) or whose diameter isfrom 2 nm and 50 nm (mesopores). The catalytic metal or metals can beGroup VIA and non-noble metal Group VIIIA metals. The Groups are givenin the Periodic Table of the Elements by Sargent-Welch ScientificCompany, No. S-18806, Copyright 1979. More particularly, the metal isselected from at least one of Mo, Co, Ni, Fe, W. More than one suchmetal can be used. Total metal loading on the catalyst may range from 4to 40 wt. % metals, based on catalyst, preferably 10 to 30 wt. %.

The support comprises one or more low acidity, ordered mesoporousmaterials, such as molecular sieve. The term “molecular sieve” refers toordered structures having pore sizes suitable for adsorbing moleculesand that are capable of separating components of a mixture on the basisof molecular size and shape differences. The low acidity, orderedmesoporous materials may be crystalline, that is having sufficient orderto provide a diffraction pattern such as, for example, by X-ray,electron or neutron diffraction, following calcination, with at leastone peak.

The term “low acidity” is used herein in the sense of a 2-methyl-2pentene reaction test and the resulting rate ratio, as described inKramer and McVicker, Accounts of Chemical Research, 19, 78 (1986), andU.S. Pat. No. 5,420,092. This scale for evaluating the acidity ofmaterials is based on the isomerization of 2-methyl-2-pentene (2MP2).The material to be evaluated is contacted with 2MP2 at a fixedtemperature, typically in the range of 200 to 250° C. The formationrates and rate ratios of the product hexene isomers of this testreaction reflect the acid site concentration and strength of thecatalyst respectively. The product hexene isomers formed include(cis/trans)4-methylpent-2-ene (4MP2), (cis/trans)3-methylpent-2-ene(3MP2), and 2,3 dimethylbute-2-ene (2,3 DMB2). 4MP2 requires only adouble bond shift, a reaction occurring on weak acid sites. 3MP2requires a methyl group shift (i.e., stronger acidity than double bondshift), whereas 2,3DMB2 requires even stronger acidity to produce asecond methyl branch. For a homologous series of solid acids,differences in 3MP2 rates normalized with respect to surface areareflect the density of acid sites possessing strengths sufficient tocatalyze the skeletal isomerization. Since skeletal isomerization ratesgenerally increase with increasing acid strength, the ratio of methylgroup migration rate to double bond shift rate (the “Rate Ratio” herein)should increase with increasing acid strength. The Rate Ratio isexpressed as the rate of (cis/trans)3-methylpent-2-ene (3MP2) over(cis/trans)4-methylpent-2-ene (4MP2). The use of the Rate Ratio, in lieuof individual conversion rates, beneficially normalizes differences inacid site populations. Thus the rate ratio of 3MP2 to 4MP2 provides auseful scale of acidity and forms the basis of the definition of “lowacidity” as that term is used herein. The rate ratio of 3MP2 to 4MP2 is“low acidity” at a ratio of 3.85 or less, preferably 3.25 or less, andmore preferably 3.00 or less. It should be noted that that these lowacidity materials will have an Alpha value of about 1. The Alpha test isdescribed in U.S. Pat. No. 3,354,078. However, the Alpha test is not assensitive for evaluating acidity as the acidity scale based on theisomerization of 2MP2. Hence two different materials may have an Alphavalue of 1 but may or may not meet the definition of “low acidity” asdefined herein. Controlling the acidity of the support provides a meansto hydrodesulfurize a naphtha feedstream while minimizing saturation ofdesirable olefins.

Where the low acidity, ordered mesoporous material contains silica andalumina, a high silica material is desired for low acidity. The silicato alumina molar ratio is preferably at least about 100, more preferablyat least about 200, and most preferably at least about 300. Supportporosity generally ranges from about 20 to about 75% by volume, or,alternatively, from about 20% to about 60% by volume. Support surfaceareas generally ranges upwards from about 20 m²/g, or alternatively,from about 20 m²/g to at least about 200 m²/g, or about 100 m²/g to atleast about 400 m²/g. Ordered mesoporous materials can accommodatesurface areas up to about 1,000 m²/g.

In an embodiment, the ordered mesoporous materials are of low acidity,inorganic, porous, non-layered, molecular sieve materials which, intheir calcined forms, exhibit an X-ray diffraction pattern with at leastone peak at a d-spacing greater than about 18 Angstrom Units (Å). Theyalso have a benzene adsorption capacity of greater than 15 grams ofbenzene per 100 grams of the material at 50 torr and 25° C. Suitableordered mesoporous materials include those synthesized using amphiphiliccompounds as directing agents. Examples of such materials are describedin U.S. Pat. No. 5,250,282. Examples of amphiphilic compounds are alsodisclosed in Winsor, Chemical Reviews, 68(1), 1968. Other suitableordered mesoporous materials are disclosed in “Review of OrderedMesoporous Materials,” U. Ciesla and F. Schuth, Microporous andMesoporous Materials, 27, (1999), 131-49. Suitable mesoporous materialsinclude, by way of example, materials designated as SBA (Santa Barbara)such as SBA-2, SBA-15 and SBA-16, materials designated as FSM (FoldingSheet Mechanism) such as FSM-16 and KSW-2, materials designated as MSU(Michigan State) such as MSU-S and MSU-X, materials designated as TMS orTransition Metal Sieves, materials designated as FMMS or functionalizedmonolayers on mesoporous supports and materials designated as APM orAcid Prepared Mesostructure.

In an embodiment, the support material is characterized by asubstantially uniform hexagonal honeycomb microstructure with uniformpores having a cell diameter greater than 2 nm and typically in therange of 2 to 50 nm, preferably 3 to 30 nm, and most preferably from 3to 20 nm. In a related embodiment, the low acidity, ordered mesoporousmaterials include the silicate ordered mesoporous materials designatedas M41S such as MCM-41, MCM-48 and MCM-50, including mixtures thereof,provided they are of sufficiently low acidity. MCM-41 can be synthesizedas a metallosilicate with Broensted acid sites by incorporating atetrahedrally coordinated trivalent element such as Al, Ga, B, or Fewithin the silicate framework. Methods of preparation are described inU.S. Pat. Nos. 5,098,684, 5,102,643 and 5,837,639.

MCM-41 is characterized by a microstructure with a uniform, hexagonalarrangement of pores with diameters of at least about 2 nm. Aftercalcination, it exhibits an X-ray diffraction pattern with at least oned-spacing greater than about 18 Å and a hexagonal electron diffractionpattern that can be indexed with a d₁₀₀ value of greater than about 18Å, which corresponds to the d-spacing of the peak in the X-raydiffraction pattern. The term “hexagonal” is intended to encompass notonly materials that exhibit mathematically perfect hexagonal symmetrywithin the limits of experimental measurement, but also those withsignificant observable deviations from that ideal state. A workingdefinition as applied to the microstructure of the ordered, mesoporoussupport material would be that most channels in the material would besurrounded by six nearest neighbor channels at roughly the samedistance. Defects and imperfections will cause significant numbers ofchannels to violate this criterion to varying degrees, depending on thequality of the material's preparation. Samples which exhibit as much as+/−25% random deviation from the average repeat distance betweenadjacent channels still clearly give images recognizable as hexagonal.

MCM-41 and similar ordered, mesoporous materials can be distinguishedfrom other porous inorganic solids by the regularity of their large openpores, whose pore size more nearly resembles that of amorphous orparacrystalline materials, but whose regular arrangement and uniformityof size (pore size distribution within a single phase of, for example,+/−25%, usually +/−15% or less of the average pore size of that phase)resemble more those of crystalline framework materials such as zeolites.

In an embodiment, the low acidity, ordered mesoporous materials used inthe catalyst support has the following composition:M_(n/q)(W_(a)X_(b)Y_(c)Z_(d)O_(h))wherein W is a divalent element, such as a divalent first row transitionmetal, e.g., manganese, cobalt and iron, and/or magnesium, preferablycobalt; X is a trivalent element, such as aluminum, boron, iron and/orgallium, preferably aluminum; Y is a tetravalent element such as siliconand/or germanium, preferably silicon; Z is a pentavalent element, suchas phosphorus; M is one or more ions, such as, for example, ammonium,Group IA, IIA and VIIB ions, usually hydrogen, sodium and/or fluorideions; n is the charge of the composition excluding M expressed asoxides; q is the weighted molar average valence of M; n/q is the numberof moles or mole fraction of M; a, b, c, and d are mole fractions of W,X, Y and Z, respectively; h is a number of from 1 to 2.5; and(a+b+c+d)=1. In an embodiment, (a+b+c) is greater than d, and h=2. Afurther embodiment is when a and d=0, and h=2. In the as-synthesizedform, the mesoporous material has a composition, on an anhydrous basis,expressed empirically as follows:rRM_(n/q)(W_(a)X_(b)Y_(c)Z_(d)O_(h))wherein R is the total organic material not included in M as an ion, andr is the coefficient for R, i.e., the number of moles or mole fractionof R. The M and R components are associated with the material as aresult of their presence during synthesis of the material and are easilyremoved or, in the case of M, replaced by post-synthesis methodshereinafter more particularly described.

To the extent desired, the original M, e.g., ammonium, sodium orchloride, ions of the as-synthesized material can be replaced, at leastin part, by ion exchange with other ions. Conventional ion-exchangemethods can be used. Replacing ions, by way of example, include metalions, hydrogen ions, hydrogen precursor, e.g., ammonium, ions andmixtures thereof. Other ions include rare earth metals and metals ofGroups IA (e.g., K), IIA (e.g., Ca), VIIA (e.g., Mn), VIIIA (e.g., Ni),IB (e.g., Cu), IIB (e.g., Zn), IIIB (e.g., In), IVB (e.g., Sn), and VIIB(e.g., F) of the Periodic Table of the Elements (Sargent-Welch Co. Cat.No. S-18806, 1979) and mixtures thereof.

In addition to the low acidity, ordered, mesoporous material, thesupport can further comprise additional materials, particularlyadditional inorganic materials. For example, inorganic materials may beused as binders, or to dilute and therefore control the amount of activemesoporous material present in the support. Inorganic diluents can beinert or, optionally, can have a catalytic functionality. Suitableinorganic diluent materials include, by way of example, alumina orsilica and the like, or precursors to these materials such asNa-silicate and Al-nitrate. In this mode of use, the particulateinorganic oxides are not acting as binder materials but are primarilyacting as bulk diluents although the material may still exert somebinding function. Though the binder function can be performed by theparticulate silicone resin, a separate binder can be used. In thecalcined state of the support, it is believed that the binder functionis provided by silica derived from the silicone resin on top of anyother binder that may be present. In the uncalcined state (e.g., thedried state), it is believed that the binding, (i.e., the greenstrength) is in part derived from the resin as is. When used as diluentsfor supports comprising molecular sieves the particulate inorganicmaterials may be present at the desired level to achieve the requisitedilution of molecular sieve. The amount of diluent material can bewithin the range of about 10 to 90 wt. %, or about 10 to 50 wt. %, orabout 20 to 50 wt. % of the combined weight of diluent and molecularsieve material in the structure. The inorganic material may also oralternatively function as an aid to mass transport into and within thestructured body. This can be advantageous when the inorganic materialhas large pores and high levels of porosity. The uncalcined bindermaterial (the silicone resin) itself is not acidic. Thus the addition ofsilicone binding material should have a dilution function on the totalacidity prior to calcination.

(II) Selective Hydrodesulfurization Processes

In another embodiment, the invention relates to a selectivehydrodesulfurization process. More particularly, the invention relatesto selective hydrodesulfurization of a naphtha boiling-rangehydrocarbon.

Naphtha feedstocks suitable for hydrodesulfurization comprise one ormore natural and/or synthetic hydrocarbons boiling in the range fromabout 50° F. to about 450° F. (10° C. to about 232° C.), at atmosphericpressure. The naphtha feedstock generally contains cracked naphtha whichusually comprises fluid catalytic cracking unit naphtha (FCC catalyticnaphtha), coker naphtha, hydrocracker naphtha, resid hydrotreaternaphtha, debutanized natural gasoline (DNG), and gasoline blendingcomponents from other sources wherein a naphtha boiling range stream canbe produced. In an embodiment, the feedstock is selected from FCCcatalytic naphtha, coker naphtha, and combinations thereof These feeds,based on olefin and sulfur content, typically benefit from selectivehydrodesulfurization.

In an embodiment, the naphtha feedstock generally contains not onlyparaffins, naphthenes, and aromatics, but also unsaturates, such asopen-chain and cyclic olefins, dienes, and cyclic hydrocarbons witholefinic side chains. The cracked naphtha feedstock generally comprisesan overall olefins concentration ranging as high as about 60 wt. %,based on feedstock, more typically as high as about 50 wt. %, and mosttypically from about 5 wt. % to about 40 wt. %. The cracked naphthafeedstock can comprise a diene concentration of as much as 15 wt. %, butmore typically ranges from about 0.02 wt. % to about 5 wt. % of thefeedstock. High diene concentrations can result in a gasoline productwith poor stability and color. The cracked naphtha feedstock sulfurcontent will generally range from about 0.05 wt. % to about 0.7 wt. %and more typically from about 0.07 wt. % to about 0.5 wt. %, based onthe total weight of the feedstock. Nitrogen content will generally rangefrom about 5 wppm to about 500 wppm, and more typically from about 20wppm to about 200 wppm.

Hydrodesulfurization using the selective hydrodesulfurization catalystscan comprise a naphtha feedstock preheating step. The chargestock ispreheated in feed/effluent heat exchangers prior to entering a furnacefor final preheating to a targeted reaction zone inlet temperature. Thefeedstock can be contacted with a hydrogen-containing stream prior to,during, and/or after preheating. The hydrogen-containing stream can alsobe added in the hydrodesulfurization reaction zone. The hydrogen streamcan be pure hydrogen or can be in admixture with other components foundin refinery hydrogen streams. It is preferred that thehydrogen-containing stream have little, if any, hydrogen sulfide. Thehydrogen stream purity should be at least about 50% by volume hydrogen,preferably at least about 65% by volume hydrogen, and more preferably atleast about 75% by volume hydrogen for best results.

The reaction zone can consist of one or more fixed bed reactors each ofwhich can comprise a plurality of catalyst beds. Since some olefinsaturation will take place, and olefin saturation and thedesulfurization reaction are generally exothermic, consequentlyinterstage cooling between fixed bed reactors, or between catalyst bedsin the same reactor shell, can be employed. A portion of the heatgenerated from the hydrodesulfurization process can be recovered, andwhere this heat recovery option is not available, cooling may beperformed through cooling utilities such as cooling water or air, orthrough use of a hydrogen quench stream. In this manner, optimumreaction temperatures can be more easily maintained.

In an embodiment, the hydrodesulfurization process uses a reactor inlettemperature below the dew point of the feedstock so that the naphthafraction will not be completely vaporized at the reactor inlet. As thehydrodesulfurization reaction begins when the naphtha feed contacts thecatalyst, some of the exothermic heat of reaction is absorbed by theendothermic heat of vaporization, thus achieving 100% vaporizationwithin the bed (dry point operation). By transferring some of the heatof reaction to vaporization, the overall temperature rise across thereactor is moderated, thus reducing the overall extent of olefinhydrogenation with only small reductions in hydrodesulfurization. Thedegree of vaporization is defined by the ratio of the inlet dew pointtemperature (T_(DP), R) of the naphtha feedstock to the reactor inlettemperature (T_(IN,) R), where R is the absolute temperature in degreesRankine. The dew point temperatures can be calculated by computersoftware programs, such as Pro/II, available from Simulation SciencesInc. In the present configuration, the T_(DP)/T_(IN) ratio should begreater than or equal to 0.990, but less than the ratio at which drypoint operation is not achieved within the catalyst bed. That is, theratio extends up to the point at which the operation stays all mixedphase in the reactor. The ratio limit may vary somewhat depending onselected operating conditions. The 0.990 ratio is specified to accountfor uncertainties in the measurement of the inlet temperature includingvariance in the location of the temperature measurement anduncertainties in the calculation of the actual dew point; however, thenaphtha feedstock should not be completely vaporized at the reactorinlet.

In an embodiment, hydrodesulfurization of the naphtha feedstocks areperformed under the following conditions:

Conditions Broad Preferred Temp (° C.) 232–371 260–354 Total Press (kPa)1480–5617 1480–3549 H₂ Feed Rate (m³/m³) 35.6–890  35.6–445  H₂ Purity(v %)  50–100  65–100 LHSV¹ 0.5–15  0.5–10  ¹Liquid Hourly SpaceVelocity

Reaction pressures and hydrogen circulation rates below these ranges canresult in higher catalyst deactivation rates resulting in less effectiveselective hydrotreating. Excessively high reaction pressures increaseenergy and equipment costs and provide diminishing marginal benefits.

(III) Methods for Making Selective Hydrodesulfurization Catalysts

The selective hydrodesulfurization catalysts are supported catalysts, inwhich the support comprises a low acidity, ordered mesoporous material.Such catalysts can be made by impregnating a low acidity, orderedmesoporous material with the catalytic metal(s). Conventional methods inwhich the catalytic metal is contained in an aqueous precursor can beused. Aqueous precursors can further comprise an organic complexingagent, as described in Chem. Soc. Chem. Commun. 22, 1684 (1987).

In an embodiment, impregnation of the hydrodesulfurizing metal or metalson the catalyst support can be performed using incipient wetnesstechniques. An amount of water to just wet all of the support isdetermined and added. The aqueous impregnation solutions are added suchthat the aqueous solution contains the total amount of hydrogenationcomponent metal(s) to be deposited on the given mass of support. Whenmore than one hydrodesulfurizing metal is to be used, impregnation canbe performed for each metal separately, including an intervening dryingstep between impregnations, or as a single co-impregnation step. Thesaturated support can then be separated, drained, and dried inpreparation for calcination.

In another embodiment, impregnation of the hydrodesulfurizing metal ormetals is on the calcined low acidity, ordered mesoporous supportmaterial which has been mixed with silicone resin. Calcination generallyis performed at a temperature of from about 480° F. to about 1,200° F.,or more preferably from about 800° F. to about 1,100° F. The lowacidity, ordered mesoporous supports have relatively low levels ofinorganic binder and have been manufactured without the addition oforganic solvents, i.e., they are free of added organic solvent. By useof the term “free of added organic solvent”, it is intended that presentsupport materials either contain no added organic solvent, or that ifamounts of organic solvents are present in the support materials, theyare present in such minor amounts that their presence will not adverselyaffect the integrity of the silica binder formed upon calcination. Theamount of solvent which any given support material may tolerate isdetermined by comparing the physical properties, especially the crushstrength, of the silica bound support material with and without theorganic solvent. It is preferred that no organic solvent be added to thesupport material. It is preferred to use water instead of added organicsolvents in the manufacturing process.

When organic solvents are omitted from the support formulation, calcinedsupports have higher compressive strength than calcined supports formedusing organic solvents. Impregnation of the calcined support can beaccomplished as described above for the catalyst support. Conventionalmethods can be used to make catalyst supports. Such methods generallyinclude the steps of mixing batch materials, which have as their mainconstituents particulate inorganic material (and, optionally, binder),blending the mixture, forming or shaping the batch into a green body,drying, and subsequently calcining the green body to form the support.Usually the forming is undertaken via extrusion or via other methodsthat require the application of pressure and/or heat such as compressionmolding. It is conventional to add such additives as lubricants,extrusion aids, plasticizers, and burnout agents (e.g., graphite) to thebatch during the mixing step which may be needed to control propertiessuch as batch viscosity. Binders, when used, can be inorganic, organic,or a combination thereof. Organic binders are temporary binders becausethey can be removed during heat-treating such as calcination, but theymay assist in maintaining the green strength of the structured bodyextrudate after extrusion. In an embodiment, the green support is freeof organic binder, and the formed and calcined support is also free oforganic binder residues. In addition to raw materials, porosity is alsodependent on the firing temperature. The higher the firing temperature,the more dense (less porous) the resulting fired structure. Conventionalextrusion procedures and equipment can be used, including the use ofextrusion aids.

In an embodiment, the support material is a low acidity, orderedmesoporous support material. Ordered mesoporous support materials can besynthesized using amphiphilic compounds, as hereinafter described, andespecially high silica/alumina ratio mesoporous materials, especiallythe high surface area mesoporous aluminosilicate and silicate materialsdesignated as M41S silica materials such as, for example, MCM-41 andMCM-48.

Such materials can be made using from a homogeneous formable mixturecomprising support material, silicone resin, optional extrusion aid andwater. The mixture components are combined to form a homogeneous orsubstantially homogeneous mixture without the addition of organicsolvent. The dry ingredients are first combined, e.g., dry blended in anintensive mixer, and then water is added in an amount to enable theformation of an extrudable mixture. Typical water amounts form a mixturethat is at least about 20 wt. % solids, or at least 30 wt. % solids, orat least about 40 wt. % solids, based on the weight of the mixture.Solids typically range from about 20 to 70 wt. % solids, or about 30 to70 wt. % solids, based on the weight of the mixture. Conventional mixingequipment, e.g., mix-muller or high shear mixers, and “noodling dies”can be used.

By way of example, some suitable mixture compositions (by weight)include about 25 to 95 wt. % support material, and about 5 to 75 wt. %silicone resin.

Extrusion aids can be added in amounts ranging from about 1 to 5 wt. %or, alternatively, about 1 to 2 wt. %, or 1.5 wt. % or less. In anembodiment, the extrudate contains sufficient support material to yielda final calcined support comprising:

-   -   (i) support material in an amount ranging from about 40 to 95        parts by weight (wt. %) or, alternatively, 70 to 95 wt. %, or 80        to 95 wt. %, and    -   (ii) silica in an amount ranging from about 5 to 60 parts wt. %        or, alternatively, 5 to 20 wt. %, or 5 to 10 wt. %, the wt. %        being based on the weight of the extrudate.

After extrusion, drying, and calcination, the extrudate comprises:

-   -   (i) support material in an amount ranging from about 50 to 99.5        parts by weight wt. % or, alternatively, about 75 to 95 wt. %,        or about 80 to 95 wt. %, or about 90 to 95 wt. %, and    -   (ii) silica in an amount ranging from about 0.5 to 50 parts by        weight wt. % or, alternatively, about 5 to 25 wt. %, or about 5        to 20 wt. %, or about 5 to 10 wt. % silica.

Such supports can be made using silicone resin of defined averageparticle size. The use of a silicone resin in this form enables thesupport material to be extruded without the use of high levels ofadditional organic or undesirable inorganic binder materials, with theminimal amount necessary of organic extrusion aids and importantlywithout the use of organic solvents. This enables green extrudates ofhigh strength to be produced. This approach also enables supportmaterials to be produced, which have high contents of active catalyticmaterial (90 wt. % or greater) and which have high compressive strengthsafter calcination. The silicone resin of defined average particle sizeis converted in-situ to a silica binder upon calcination. The resultantcalcined support material contains a primarily low acidity silicabinder, which is highly desirable for many applications, especiallywhere the support material comprises ordered, mesoporous materials.

Conventional silicone resins can be used. In an embodiment, the siliconeresin is used in particulate form as opposed to an emulsion, or asolution or in the form of flakes. The particulate silicone resins ofthis embodiment have the following properties:

-   -   (i) The particulate silicone resins can have an average particle        size of about 700 μm or less, preferably about 600 μm or less.        Expressed in terms of a range, the average particle size of the        particulate silicone resin can range from about 0.01 to about        700 μm or, alternatively, about 0.02 to about 600 μm, or about        0.1 to about 450 μm.    -   (ii) The particulate silicone resins have a minimum particle        size ranging from at least about 2 μm to at least about 25 μm.    -   (iii) The particulate silicone resin remains solid at ambient        temperature (i.e., room temperature or below the forming        temperature used to prepare the support, e.g., below the        extrusion or compression molding temperature).    -   (iv) The particulate silicone resins can have a softening point        such that under the selected pressures and temperatures of        forming, e.g., extrusion or compression molding, it melts or        flows or is able to coalesce. The silicone resin can re-solidify        on cooling after extrusion or compression molding.    -   (v) The particulate silicone resins can have a silicon oxide        content of at least 50% by weight and a degree of cross-linking        of 1.5 or less or, alternatively, 1.3 or less, or 1.2 or less.    -   (vi) The particulate silicone resins can have a viscosity of at        least about 20 centipoise (60% solids in toluene, though the use        of a solvent is optional) or, alternatively, at least about 30        centipoise, or at least about 50 centipoise.    -   (vii) The particulate silicone resins have a weight average        molecular weight within the range of about 1000 to 10,000 or,        alternatively, about 2000 to 7000, or about 2000 to 4000.    -   (viii) The particulate silicone resins have a silanol content of        at least about 3 wt. % or, alternatively, at least about 5 wt. %

The silicone resin can be a single silicone resin or a combination ofsilicone resins which meet the above criteria. Silicone resins includepolysiloxanes containing a repeating silicon-oxygen backbone and organicgroups attached to a proportion of the silicon atoms by silicon-carbonbonds, including linear, branched and/or cross-linked structures. Silanemonomers are the precursors of silicones and the nomenclature ofsilicones makes use of the letters M, D, T and Q to representmonofunctional, difunctional, trifunctional and quadrifunctional monomerunits. Primes, e.g., D′ are used to indicate substituents other thanmethyl. Examples of formulas and their corresponding symbols forsilicones are provided in Table 1.

TABLE 1 Formula Functionality Symbol (CH₃)₃SiO_(0.5) Mono M (CH₃)₂SiO DiD (CH₃)SiO_(1.5) Tri T (CH₃)(C₆H₅)SiO Di D′ (CH₃)(H)SiO Di D′ SiO₂Quadri Q

In an embodiment, the silicone resins are the polysiloxanes with alkyland/or aryl and/or glycol groups. The alkyl groups can include 1 to 12carbons, and more particularly 6 to 10 carbons. The resins can becross-linkable silicones containing reactive silanol groups. Examples ofsuitable silicone resins are those that originate from methyl hydrogenpolysiloxane and phenyl methyl polysiloxanes. High activity siliconescan be used, such as Dow Corning Q6-2230 silicone resin, sometimesreferred to as Dow Corning® 233 flake resin.

After forming, e.g., by extrusion, the resulting-shaped, green materialcan be optionally dried to remove the water used in forming thecomposition mixture. Conventional drying methods can be used, alone orin combination. Drying times range for a period of about one minute toabout 12 hours or more. In an embodiment, drying is accomplished byplacing the green material in an oven at a temperature in the range of50° to 100° C., or 90° to 100° C. Drying forms a crack-free,self-supporting structure. The support is calcined following extrusionand optional drying.

During calcination, the silicone resin is converted to silica, whichacts as an inorganic binder for the particulate inorganic material inthe calcined support. Conventional calcination conditions and equipmentcan be used. For example, the extrudate may be calcined in anoxygen-containing atmosphere, preferably air, at a rate of 0.2° C. to 5°C./minute to a temperature greater than 300° C. but below a temperatureat which the crystallinity of the molecular sieve is adversely affected.Generally, such temperature will be in the range of from 400° C. to1000° C., preferably below 600° C. Preferably the temperature ofcalcination is within the approximate range of 350° C. to 550° C. Theproduct is maintained at the calcination temperature usually for 1 to 24hours.

In an embodiment, the dried support body is first calcined at atemperature in the range of 400° C. to 1000° C., preferably 400 to 600°C., most preferably 450 to 550° C., in an inert atmosphere, which ispreferably flowing nitrogen. The preferred flow rate is within the rangeof 1 to 10 v/v/hr, preferably 2 to 8 v/v/hr and most preferably is aflow rate of 5 v/v/hr. The first stage is undertaken for between 1 to 24hours, preferably 1 to 10 hours and most preferably for 2 hours. Thisfirst stage is then followed by a second calcination stage in anoxidizing atmosphere; preferably the oxidizing atmosphere is 100% air.The second stage is undertaken for a period of 1 to 24 hours, preferably1 to 12 hours and most preferably for between 6 to 13 hours. The flowrate for the oxidizing gas is within the range of 1 to 10 v/v/hr,preferably 2 to 8 v/v/hr and most preferably is a flow rate of 5 v/v/hr.The temperature of the second stage is within the range 400° C. to 1000°C., preferably 400 to 600° C., most preferably 450 to 550° C. Theswitchover from the first stage to the second stage is gradual and istypically undertaken over a period of 1 to 10 hours, more preferably 1to 5 hours and most preferably 2 to 4 hours.

While not wishing to be bound by any theory or model, it is believedthat the use of a silicone resin enables the particulate inorganicmaterial to be extruded without the use of high levels of additionalorganic or undesirable inorganic binder materials, without excessiveamounts of organic extrusion aids, and without the use of organicsolvents. The resulting support materials can have high contents ofmesoporous support material (90 wt. % or greater) and retain a degree ofcompressive strength after calcination. Since calcination convertsin-situ the silicone resin of defined average particle size to a silicabinder, the resultant calcined support contains particulate inorganicmaterial in the presence of a primarily low acidity silica binder.

The most common binder for molecular sieves is alumina. Using silica asa binder in molecular sieves is difficult and is not simply a matter ofreplacing alumina with silica. Conventional silica binders typicallyinvolve the use of caustic and water with the silica gel and powderedsilica in the preparation of the silica binder. In the case ofmesoporous materials of the M41S family, caustic may damage the supportstructure. Moreover, MCM-41S family members, e.g., MCM-41, have highsorption capacity and thus require large amounts of water. This leads toprocessing difficulties such as over peptizing and solidifying beforethe mesoporous material can be extruded. Moreover, the use of aluminabinders can alter the overall acidity of the support material. Aluminais more acidic than silica, thus resulting in a support that can besufficiently acidic to cause significant olefin saturation during thehydrodesulfurization process.

In an embodiment, hydrodesulfurization metals can be added followingcalcination of the mesoporous support materials. Impregnation of thehydrodesulfurizing metal or metals on the catalyst support can beperformed using incipient wetness techniques. An amount of water to justwet all of the support is determined and added. The aqueous impregnationsolutions are added such that the aqueous solution contains the totalamount of hydrogenation component metal(s) to be deposited on the givenmass of support. When more than one hydrodesulfurizing metal is to beused, impregnation can be performed for each metal separately, includingan intervening drying step between impregnations, or as a singleco-impregnation step. The saturated support can then be separated,drained, and dried.

The following examples are presented to illustrate the invention andshould not be considered limiting in any way.

EXAMPLE 1

Catalyst Support Preparation

A mixture was prepared for extrusion by blending about 90 wt. % ofMCM-41 crystal that had been calcined, and 10 wt. % SiO₂ equivalent ofDow Corning 6-2230 silicone resin (which had been milled to <30 USmesh), in an Eirich mixer for 5 minutes. Water was added to adjust thesolids in the mixture to 42 wt. % and 1.5 wt. % polyvinylalcohol wasadded as an extrusion aid. This mixture was allowed to ball up into1/16″ to ⅛″ spheres prior to extrusion. The extrusion was run with a1/16 cylinder die plate and at 11.5 amps. During the extrusion, steamwas given off and there was noticeable condensation on the outsidesurface of the die. The extrudate was dried at 250° F. overnight and wasthen calcined in nitrogen followed by air. The compressive strengthafter calcination was measured as 54 lb/in₂.

EXAMPLE 2

Support Acidity Measurements

Potential catalyst support samples were evaluated for acidity inaccordance with a 2-methyl-2 pentene reaction test. As discussed,skeletal isomerization rates generally increase with relative increasingacid strength, and consequently, the ratio of methyl group migrationrate to double bond shift rate (the “Rate Ratio” herein) increases withincreasing acid strength. The equilibrium value for the ratio of(cis/trans)3-methylpent-2-ene (3MP2) to (cis/trans)4-methylpent-2-ene(4MP2) is near 4.4. It should be noted that Support A, which is anamorphous silica-alumina, has an acidity on the alpha scale of about 1,corresponding to a Rate Ratio value of approximately 3.85.

The tests were conducted under the following conditions: 250° C.temperature, 1.0 atm. pressure, 1.0 g catalyst, 2.0 hours on feed, witha feed comprising 11.2 ml/min. of 2-methyl-2 pentene and 150 m/min. ofhelium.

Support A comprised 87 wt. % silica and 13 wt. % alumina and is theamorphous silica-alumina Davison MS-13. Support B comprised Davisilamorphous silica powder of unknown purity. Support C comprised MCM-41containing 90.7 wt. % silica and 9.3 wt. % alumina without binder.Support D comprised MCM-41 containing 99.7 wt. % silica and 0.3 wt. %alumina without binder. Support E comprised 35 wt. % alumina binder and65 wt. % Support D (MCM-41 containing 99.7 wt. % silica and 0.3 wt. %alumina). Support F comprised 10 wt. % silica binder and 90 wt. %Support D (MCM-41containing 99.7 wt. % silica and 0.3 wt. % alumina).

Feed Rate Ratio Sup- Conversion CT4MP2 rate CT3MP2 rate (Equilibriumport (Mol. %) (Mol/hr/g × 10³⁾ (Mol/hr/g × 10³⁾ 4.4) A 73.6 2.57 9.903.85 B 24.0 0.05 0.017 0.34 C 77.5 2.18 9.25 4.24 D 65.2 3.08 8.42 2.73E 75.4 2.38 9.97 4.20 F 45.7 4.03 1.63 0.40

As stated above, Support A, which is an amorphous silica-alumina, has anacidity measured by the alpha test of about 1. The acid catalyticactivity of a zeolite may be measured by its “alpha value”, which is theratio of the rate constant of a test sample for cracking normal hexaneto the rate constant of a standard reference catalyst (U.S. Pat. No.3,354,078 and in The Journal of Catalysis, Vol. IV, pp. 522-529 (August1965), both of which are incorporated herein by reference). The alphatest is insensitive to differentiation of the very low levels of aciditydiscerned in the 2-methyl-2 pentene reaction test, differences whichaffect selectivity for olefin saturation during HDS. That is, the RateRatio values less than the amorphous silica-alumina value in the2-methyl-2 pentene reaction test (approximately 3.85) would all bereported at 1 in the alpha test. Thus, on the typical alpha acidityscale, it is necessary but not sufficient to have the lowest measuredacidity value, alpha value=1.

The amorphous silica sample, Support B, has a low acidity compared withthe amorphous silica-alumina (Support A). The framework aluminacontaining MCM-41, Support C shows a high acidity, nearly at theequilibrium value. The same mesoporous material prepared withoutalumina, Support D, is characterized by a low acidity value. Thissupport can further be formulated with a binder to achieve Support E andSupport F. It is clear from this example that the addition of aluminabinder to the MCM-41 material, Support E, results in much higher aciditythan the MCM-41 material bound with silica, Support F. In these examplesSupports A, C and E are too acidic for use as the catalyst support.

EXAMPLE 3

Catalyst Acidity Measurements

Catalyst A comprised Support D (MCM-41 containing 99.7 wt. % silica, 0.3wt. % alumina) with approximately 7.4 wt. % CoO and 28.5 wt. % MoO₃.Catalyst B comprised Support C (MCM-41 containing 90.7 wt. % silica and9.3 wt. % alumina) with approximately 7.4 wt. % CoO and 28.5 wt. % MoO₃.Catalysts were evaluated in the oxide form. Test results are set out inthe following table.

Feed Conversion CT4MP2 rate CT3MP2 rate Rate Catalyst (Mol. %) (Mol/hr/g× 10³⁾ (Mol/hr/g × 10³⁾ Ratio A 39.0 2.79 0.95 0.34 B 44.4 3.41 2.040.60

Catalyst A, comprising MCM-41 of the highest silica content compared tothe other MCM-41 catalyst, has the lowest acidity. Catalyst B, whichcontains some alumina, has an appreciably higher acid strength, but isstill low acidity as that term is used herein. Although the measuredacidities for both of these catalysts are considered low, the inherenthigher acidity of the support used to prepare Catalyst B results inhigher acidity in the final catalyst. This comparison illustrates thatthe support acidity should be used as the indicator of acidity for thepurpose of choosing a suitable support to achieve high selectivity. Theexample below will illustrate that the higher acidity of the supportmanifests as diminished catalyst selectivity in a catalyst performancetest.

EXAMPLE 4

Comparison of Acidity on Catalyst Selectivity

In a micro-unit model feed test, catalysts were evaluated on a feedconsisting of 36% Hexene-1, 32% n-Heptane, 32% Toluene, 1950-2000 wppmSulfur as Thiophene, and 19 wppm Nitrogen as Tetrahydroquinoline.Reaction conditions were 200 psig total reaction pressure, WHW=14.7,H₂/feed=6.1. Catalysts were presulfided in a separate reactor andtransferred for model feed analysis.

Catalyst C is a CoMo/MCM-41 catalyst (7.4% CoO and 28.5% MoO₃) on MCM-41containing 99.7 wt. % silica and 0.3 wt. % alumina (Catalyst A) and hasbeen sulfided prior to use. Catalyst D is a CoMo/MCM-41 catalyst (7.4%CoO and 28.5% MoO₃) on MCM-41 containing 90.7 wt. % silica and 9.3 wt. %alumina (Catalyst B) which has also been sulfided prior to use.

The relative rates of HDS to olefin saturation (OSAT) were calculated asthe natural log of the inverse of the normalized fraction of sulfur orolefins remaining in the product. The selectivity ratio presented in theFIGURE is the ratio of these two values.

The alumina containing catalyst, Catalyst D, shows lower selectivitythan the lower acidity siliceous catalyst, Catalyst C. As one familiarwith the art would observe, both these catalysts would traditionally beconsidered to demonstrate high selectivity towards retention of olefins.In this invention, we distinguish those supports characterized by RateRatio values measurably below the equilibrium value 4.4 (ratio of(cis/trans)t-3-methylpent-2-ene (t-3MP2) to(cis/trans)4-methylpent-2-ene (4MP2)), preferably below the value foramorphous-silica alumina (approximately 3.85) from those with valuesnear the equilibrium as measured in accordance with a 2-methyl-2 pentenereaction test. In this example, the support used to prepare Catalyst C(Support D) has a much lower acidity than the support used to prepareCatalyst D (Support C). This difference in support acidity is observedin the performance of the catalyst as selectivity for olefin retention.

EXAMPLE 5

Comparison of Mesoporous Order (Ordered versus Amorphous) on CatalystSelectivity

Catalysts were tested in a small pilot plant on an intermediate catnaphtha feed. Catalyst A comprised Support D (MCM-41) containing 99.7wt. % silica, 0.3 wt. % alumina) with approximately 7.4 wt. % CoO and28.5 wt. % MoO₃. Catalyst E comprised Support B (Davisil amorphoussilica powder of unknown purity) with approximately 7.4 wt. % CoO and28.5 wt. % MoO₃ The reactors were loaded with 4.0 cc of catalyst. Thecatalysts were sulfided with a 10% H₂S/H₂ gas blend at approximately a10 L/hr gas rate at 1652 kPa (225 psig) for two 12-hour holding periodsat temperatures of 204 to 343° C. (400° F. and 650° F.). Temperature wasreduced to 93° C. (200° F.) and 100% H₂ was introduced into the reactorfollowed by the intermediate cat naphtha feed. The test was performed inan isothermal, downflow, all-vapor-phase pilot plant. The intermediatecat naphtha had a 5/95% boiling range of 68 to 186° C. (155 to 367° F.),1425 wppm total sulfur, 33 wppm nitrogen, and 64.6 bromine number. Thecatalysts were allowed to line out on feed at 274° C. (525° F.) and 1652kPa (225 psig) before the test. Test reactor conditions were 302° C.(575° F.), 356 m³/m³ (2000 scf/B), 100% hydrogen treat gas, 1652 kPa(225 psig) total inlet pressure, and an LHSV of 5.4 hr⁻¹. Product fromcatalyst A had 97.73% sulfur removal and a 33.13% bromine numberreduction. Product from catalyst E had 96.44% sulfur removal and a41.18% bromine number reduction.

At greater HDS, the catalyst based on the mesoporous-ordered (MCM-41)support saturated fewer olefins (shows greater selectivity) than thecatalyst based on an amorphous support. Co/Mo catalyst on a mesoporousMCM-41 support is more selective than a Co/Mo reference catalyst on anamorphous support, i.e., the mesoporous catalyst has a higher HDS/OSAT(olefin saturation) ratio than the reference catalyst. Although theamorphous support had a lower equilibrium rate ratio in the acidity testin Example 1, the catalyst based on this support is less selective(saturates more olefins) than the catalyst based on themesoporous-ordered support. The novel structure of mesoporous-orderedsupports increases the selectivity performance of the final catalyst.

1. A selective hydrodesulfurization catalyst comprising at least onehydrodesulfurizing metal supported on a low acidity, ordered mesoporoussupport material and bound with a silica binder derived from siliconeresin, the low acidity ordered mesoporous support having a Rate Ratio ofless than about 3.25.
 2. The catalyst of claim 1 wherein thehydrodesulfurizing metal is a Group VIA metal, a non-noble Group VIIIAmetal, and combinations thereof.
 3. The catalyst of claim 2 wherein thecatalyst contains from about 4 to about 40 wt. % of hydrodesulfurizingmetal, based on catalyst.
 4. The catalyst of claim 3 wherein the silicabinder is derived from a silicone resin having an average particle sizeof about 700 μm or less.
 5. The catalyst of claim 4 wherein the siliconeresin has an average molecular weight of from about 1,000 to about10,000.
 6. The catalyst of claim 1 wherein the mesoporous support is lowacidity MCM-41.
 7. The catalyst of claim 2 wherein thehydrodesulfurizing metal comprises Co and Mo.
 8. The catalyst of claim 1wherein the low acidity mesoporous support has a Rate Ratio less thanabout 3.00.
 9. The catalyst of claim 1 wherein the catalyst has beensulfided.
 10. A selective hydrodesulfurization catalyst comprising atleast about 10 wt % and less than about 40 wt % of hydrodesulfurizingmetal supported on a low acidity, ordered mesoporous support materialand bound with a silica binder derived from silicone resin, the lowacidity ordered mesoporous support having a Rate Ratio of less thanabout 3.85.
 11. The catalyst of claim 10 further comprising sulfidingthe metal-impregnated low acidity, ordered mesoporous support undersulfiding conditions for a sulfiding time.
 12. The catalyst of claim 10wherein in step (a), the low acidity, ordered mesoporous supportmaterial is combined with silicone resin and water.
 13. The catalyst ofclaim 10 wherein the combining of the low acidity, ordered mesoporoussupport material wit silicone resin is free of added organic solvent.14. The catalyst of claim 10 wherein the hydrodesulfurizing metal is aGroup VIA metal, a non-noble Group VIIIA metal, and combinationsthereof.
 15. The catalyst of claim 10 wherein the silica binder isderived from a silicone resin having an average particle size of about700 μm or less.
 16. The catalyst of claim 15 wherein the silicone resinhas an average molecular weight of from about 1,000 to about 10,000. 17.The catalyst of claim 10 wherein the mesoporous support is low acidityMCM-41.
 18. The catalyst of claim 10 wherein the hydrodesulfurizingmetal comprises Co and Mo.
 19. The catalyst of claim 10 wherein the lowacidity mesoporous support has a Rate Ratio less than about 3.25. 20.The catalyst of claim 19 wherein the low acidity mesoporous support hasa Rate Ratio less than about 3.00.